Many structures are built on foundations or slabs made of concrete poured on a grade of soil. Changes in the weather and moisture levels in the soil may cause the foundation to buckle or crack. The shifting of the soil occurs for a variety of reasons, including uneven changes in the water content of the supporting soil, uneven compacting of the soil, and uneven loads placed on the grade. Various techniques are employed to level and repair foundations that have been damaged.
Another approach has been to pour the foundation on a prepared grade, then raise the foundation a selected distance above the grade before building a structure on the foundation. In this technique, piers are first installed in soil below the grade at various positions. The upper end of each pier will be at or near the grade level. Then, forms are placed on the piers to serve as lifting stations after concrete is poured. A slab foundation may have numerous lifting stations to provide adequate support during and after being lifted. A hydraulic jack or screw jack may be employed with each lifting station to lift the slab foundation. To avoid damage to the foundation while it is being lifted, it is important to keep the foundation substantially level.
U.S. Pat. No. 8,834,072 teaches a method of pouring a slab foundation on fill materials or a variety of forms. After the concrete hardens, the fill material and/or forms are removed from under the slab foundation. This technique results in the foundation being at an elevation above the grade without having to lift it.